Communication devices such as wireless devices are also known as, e.g., User Equipments (UE), mobile terminals, wireless terminals and/or mobile stations. Wireless devices are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system, wireless communications network, or cellular network. The communication may be performed, e.g., between two wireless devices, between a wireless device and a regular telephone, and/or between a wireless device and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Wireless devices may further be referred to as mobile telephones, cellular telephones, laptops, tablets or surf plates with wireless capability, just to mention some further examples. The wireless devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another wireless device or a server.
The wireless communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by an access node such as a base station, e.g., a Radio Base Station (RBS), which sometimes may be referred to as, e.g., “Evolved Node B (eNB)”, “eNodeB”, “NodeB”, “B node”, or Base Transceiver Station (BTS), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the wireless device. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the wireless device to the base station.
The consideration of automatic features has become a key element in the definition of new generation mobile networks in the last few years. The 3 rd Generation Partnership Project (3GPP) has included Self-Organizing Networks (SONs) as part of recent standards of mobile communications networks, also known as wireless communications networks, such as LTE (Long Term Evolution).
The SON functionalities are classified into three groups: Self-Configuration, Self-Optimization and Self-Healing. Self-Configuration functions aim to automatically define the configuration parameters of a network in the planning phase or when a new equipment is added to an existing infrastructure in the operational phase. The objective of Self-Optimization functions is to modify network parameters adapting the network to different environment conditions without human intervention. Self-Healing functions carry out the detection, diagnosis, compensation and recovery of network performance failures in an automatic manner.
One of the fundamental functions in Self-Healing is Cell Outage Detection (COD). A cell is in outage when it cannot carry traffic due to a failure. In this situation, it is very important to find out the cell outage as soon as possible to minimize the effects in the network.
There are several methods to implement COD. In most cases [1][2], the COD algorithm monitors Key Performance Indicators (KPIs) and alarms reported by cells to determine if they experience problems. KPIs are high-level indicators that may be obtained from performance counters in a wireless communications network. The performance counters may be measurements made by users, e.g., wireless devices, or base stations, that provide information about a cell and the network performance. In [3], the authors present a COD algorithm to detect outages based on the analysis of the KPIs reported by each cell, which allows to determine if any of its neighbor cells is in outage. In [4], a COD algorithm based on user measurements is presented. In an LTE network, the cells are controlled by an eNB. An eNB is a kind of radio access server controlling one or more, typically 3, radio cells, wherein each radio cell comprises one or more radio transmitter and radio receiver antennas, and wherein the radio connection of a terminal, e.g., a UE, to a telecommunications system is served by a certain cell of a certain eNB. When an eNB suspects that an own cell may be in outage, it requests a neighbor cell to gather measurements from the potential cell in outage. If this is not possible, the controlling eNB concludes that the cell is in outage. The COD algorithm proposed in [5] is based on the neighbor cell list reports which are able to detect cell outages in short time periods.
When there is a cell in outage in a network, different situations may occur. On the one hand, in some cases, the fault that causes the outage affects only the cell in outage. In this situation, the related eNB can provide the KPIs from this sector indicating that the sector is not available due to a problem. On the other hand, in other cases, the outage affects the entire eNB. When this occurs, there are no KPIs available in the OSS (Operations Support System) from any cell of the outage site. If the detection algorithm is based on monitoring the value of different KPIs of each cell, this outage situation cannot be detected.
In [1][2], the detection is based on KPIs and alarms reported by cells. With this methodology, it is possible to detect outage situations only if the eNB can supply KPIs from the outage cell to the OSS. However, if the outage affects the eNB, no KPIs will be available from the outage cell.
In [3], the authors present a COD algorithm based on the KPIs reported by each cell which allows determining if any of its neighbor cells is in outage. The effectiveness of this algorithm depends on the level of degradation in other cells caused by the cell in outage. This is an important limitation of the algorithm because in many cases a cell in outage does not cause a performance degradation in the neighbor cells.
Using the algorithm presented in [4], the outage problem cannot be detected if the outage affects the eNB because the measurement request cannot be sent.
The COD algorithm proposed in [5], is based on information reported on user traces and this feature is the main drawback of this approach because the use of traces limits the bandwidth of the system and operators are unwilling to activate them.
Thus, existing COD methods are inadequate for cell outage detection, especially when the eNode serving the affected cell is also affected, which leads to degradation of the wireless communication method.